Method for producing maize flour

ABSTRACT

This invention provides a novel method for producing maize flour including at least one treatment step in which a product comprising maize is treated under alkaline conditions, wherein an alkaline solution is sprayed onto the product. Furthermore, a facility for producing maize flour is disclosed, in particular in said method. Moreover, maize flour obtained by this method and foodstuffs containing this flour are disclosed.

Maize is a plant from the botanical family of the Poaceae and representsone of the most important cereal grains. The plant has its origin inMexico. After the discovery of America by Christopher Columbus, maizewas brought to Europe. In areas with high consumption of maize, a newdisease—today known as Pellagra—has been observed. Pellagra is caused bya deficit of niacin. In countries where maize is a daily staff of life,the so-called nixtamalized corn is produced by the steps of alkalinecooking of corn (in particular in a lime solution), washing, wet millingthe nixtamal, and drying, thereby producing corn maize flour in order toprohibit said deficiency symptoms. Flour produced by this method isusually called masa flour in the US and nixtalamizado in Mexico.

Besides the niacin release, the nixtamalization process comprises otherpositive effects. The most important biochemical changes during thenixtamalization process are:

increase in the calcium level with improvement in the Ca to P ratio;

swelling and gelatinization of starch;

decrease in insoluble dietary fiber and zein protein;

an improvement of the leucine to isoleucine ratio, reducing therequirement for niacin;

niacin-release from pericarp/aleuron/endosperm;

reduction or elimination of bacterial contamination.

Moreover, functional changes—especially by the addition of lime asalkali—can be observed as having beneficial influence on the taste, theviscosity and elasticity and the color of a tortilla dough prepared fromthe flour.

The main edible product produced from the nixtamalized corn flour is thetortilla, which is a flat, round, unfermented and baked thin pancake.

Many conventional processes are described wherein the maize corn iscooked in an alkaline solution for many hours with the disadvantages ofhigh energy demand for cooking and time- and energy-demanding wastewatertreatment (e.g. in WO 03/063594 A2 and WO 02/056706 A1).

Several preparations of nixtamalized maize flour have therefore beendeveloped by means of moist-heat cooking without wastewater production.In this production process, the raw materials water and alkali, inparticular lime, and saturated steam as energy source are added in aprecise and controllable dosage.

In WO 2007/076356 A2, such a preparation without occurring wastewater isdisclosed for masa harina, whereby after one preconditioning step byspraying water, milling and sifting of the fine grind, said sifted finegrind has to be mixed with lime powder in order to receive a limed grindbefore moist-heat cooking.

U.S. Pat. No. 6,326,045 B1 also comprises a method for the production ofcorn flour by moist-heat cooking without wastewater. It is proposed tomix the flour finally with lime powder to obtain instant masa flour.

U.S. Pat. No. 4,463,022 describes grain with added lime powder fed in agrinding chamber. Next to the downsizing of the grain, lime isdistributed into the product by this process simultaneously.

When lime is added in powder form, it has to be homogeneouslydistributed on the surface of the corn by mechanical means as describedin the prior art, which leads to an additional energy consumption.Moreover, the use of such mechanical means still does not ensure thatthe lime is distributed as homogeneously as necessary in order toprohibit any local concentration differences. Such local concentrationdifferences lead to the fact that said important biochemical changes donot take place homogeneously or sufficiently in the whole product,having a negative influence on the quality of the maize flour, finally.

It is therefore an object of the present invention to avoid thedisadvantages as described above. In particular, it is an object of thepresent invention to provide a method for producing maize flour whichhas a homogeneous lime distribution and which at the same time does notrequire additional waste water treatment and which is thereby cost andenergy efficient.

Surprisingly, it has been found that spraying an alkaline solution,especially a lime solution, onto a product comprising maize solves thisproblem. This spraying step will subsequently be referred to as thetreatment step. In particular, the lime is distributed homogeneouslyover the surface of the product, which minimizes local concentrationdifferences without the need of an additional device for mixing theproduct with lime powder. Moreover, when solved in water, the alkali, inparticular lime, can pass the surface into the corn to even improve thedistribution in relation to the final product over the duration of thistreatment step.

Prior to spraying the alkaline solution onto the product, the corn maybe washed by any method, in particular by any conventional method.

Preferably, the alkaline solution comprises water and between 1 and 5%by weight, more preferably between 2 and 4% by weight of lime.

The method may further comprise at least one preconditioning steppreceding said treatment step, in which preconditioning step the productis moistened, in particular with water. Due to this preconditioning, thecorn kernel is mellowed. The at least one preconditioning step, inparticular each preconditioning step, may take between 2.5 and 12 hours,preferably between 3 and 10 hours. This time range guarantees that thecorn kernel is mellowed sufficiently for a further optional millingstep.

The method may comprise at least a first preconditioning step and asecond preconditioning step, wherein the product is ground coarselybetween the first preconditioning step and the second preconditioningstep. This coarse milling increases the surface of the product andthereby facilitates the entry of water in the second preconditioningstep. Preferably, during coarse grinding, the particles are ground toparticle sizes in the range between 1000 μm and 6000 μm, more preferablybetween 1500 μm and 5500 μm.

The coarse grinding can be performed, for example, by a roller mill, inparticular a four-roller mill.

After coarse grinding and preferably before the second preconditioningstep, a fine fraction of the product may be removed by classifying, inparticular by air-classification or sieving with a plan sifter(“Plansichter”). During this classification, particles having sizesbelow 1000 μm, preferably below 1500 μm can be removed from the product.

By the second preconditioning step, in which the received product ismoistened with water, the water content in the hull and bran fractioncan be further increased. When the time of the second preconditioningstep is between 2.5 and 12 hours, preferably between 3 and 10 hours, acomplete mellowing of the whole corn kernel is achieved, in particularto a water content of 20 to 30 wt %.

Subsequent to the second preconditioning step, the obtained product issubjected to the treatment step where it is sprayed with the alkalinesolution, in particular the lime solution. Preferably, the alkalinesolution is added to the product in an amount of 2 to 6%, preferably 3to 5% by weight of dry matter of maize. Alkali or especially lime leadsto diverse beneficial biochemical changes as described. The surface ofthe product is moistened with the solved alkali, in particular lime,with the advantages as described above, such as a homogeneousdistribution of the lime within the flour.

The treatment step with alkaline, in particular lime solution, may befollowed by a hydro-thermal treatment, in particular by steaming. Thishydro-thermal treatment removes the diffusion barrier comprised by thehull fraction of the corn kernels allowing the alkali to soften andswell endosperm, germ and bran fractions. Moreover, this hydro-thermaltreatment is necessary to intensify the biochemical changes by alkali,in particular lime as described, such as degradation of insoluble zeinprotein.

During the hydro-thermal treatment, the product may be heated to atemperature between 80 and 105° C., preferably between 95 and 100° C.

In some embodiments, the hydro-thermal treatment is performed in atwo-stage process comprising at least a first hydro-thermal treatmentstep and a second hydro-thermal treatment step.

During the second hydro-thermal treatment step, the product undergoesbiochemical changes such as protein degradation, especially a decreaseof insoluble zein protein, which are intensified. Moreover, the secondhydro-thermal treatment step also serves hygienic purposes byelimination of bacteria and/or pathogens.

At least part of the hydro-thermal treatment, in particular at least thesecond hydro-thermal treatment step, may be performed continuously.During hydro-thermal treatment by steaming, the product can be contacteddirectly with saturated steam at a temperature of 80-105° C., preferablyat 95-100° C.; this may apply to any one or to both hydro-thermaltreatment steps. Furthermore, during hydro-thermal treatment bysteaming, the product may be contacted directly with saturated steam for30-90 minutes (both hydro-thermal treatment steps taken together).

Preferably, the hydro-thermal treatment is followed by a holding time ofat least 10 minutes, preferably at least 60 minutes, most preferably atleast 90 minutes. This holding time, which can take place betweensteaming and an optional subsequent flaking step, serves for equalizingthe temperature and moisture in the individual maize kernels, as well asimproving the elasticity of the product, thereby facilitating downstreamprocessing.

Furthermore, the method can comprise at least one flaking step in whichthe product is flaked. This flaking step can take place after thehydro-thermal treatment or holding time. By this flaking step, theproduct can be prepared for an optional subsequent drying step. Inparticular, a further bursting of the (insoluble) hull fraction bymechanical means can be obtained. Additionally, the surface of thereceived product can be increased by flaking, allowing optimized drying.Moreover, the starch structure is damaged, which proved advantageous indownstream processing.

The method may further comprise at least one drying step, in particularafter the hydrothermal treatment or after the holding time or after theflaking step. By lowering the water content of the product in at leastone drying step, the shelf-life of the final maize flour product can beprolonged. The water content is preferably reduced to lower than 12 wt%.

The product may be dried by hot-air or thermo-pneumatic drying. The hotair may be indirectly generated by an air-heater. The exhausted hot-airmay be extracted.

At least one drying step can be performed in a fluidized bed dryer or aroaster. By the cross-flow occurring in this dryer, hot air is contactedto the product more efficiently and the water content can be furtherdecreased. Preferably, the method contains a first drying step performedin a hot-air drier and a second step performed in a fluidized bed drieror a roaster.

The method can further comprise at least one cooling step, in particularafter the drying step. Cooling may be performed by cool-air drying ofthe product. This cooling step also results in a further reduction ofthe water content.

A subsequent milling step guarantees a uniform product specification ata certain degree of granulation. A hammer mill or a roller mill aresuitable to perform this milling step in an accurate way.

A further aspect of the present invention is related to a facility forproducing maize flour, in particular in a method as described above.This facility includes at least one preconditioner, preferably at leasttwo consecutive preconditioners, for moistening a product comprisingmaize flour. At least one of the preconditioners may contain at leastone spraying device for homogeneously spraying fluids onto the cornkernels.

Moreover, the facility comprises at least one further preconditioner forspraying an alkaline solution onto the product, in particular a limesolution. The further preconditioner also contains at least one sprayingdevice. For the treatment step with alkali, this spraying devicepreferably comprises or consists of materials that resist to a broad pHrange, especially to alkaline conditions. Preferably, the surface wallsof the facility which can get into contact with the product limedproduct also comprise or consist of such a material or materials. Thepreconditioner may also contain provisions for measuring and adjustingthe temperature. The usage of three consecutive preconditioners allows adownstream process without any need for refeedings.

In addition, the facility comprises at least one steamer for steamingthe product, in particular with saturated steam, and at least one dryerfor drying the product, in particular at least one air-heater and/or atleast one fluidized bed dryer and/or at least one roaster.

The facility may further comprise at least one of the following:

at least one flaking device arranged between the at least onehydro-thermal device and the at least one dryer, for flaking theproduct;

at least one cooling device arranged downstream of the dryer, forcooling the product;

at least one classifying device, in particular downstream of the dryeror the cooling device, for removing a fraction comprising particleshaving sizes preferably below 1000 μm;

at least one milling device, in particular downstream of the dryer orthe cooling device or the classifying device, for milling the product,in particular a hammer mill or a roller mill.

These features allow the performance of the respective method steps asdescribed above.

The invention is further related to a maize flour obtained by a methodas described above and/or by a facility as described above. This maizeflour has a better quality than those known from the prior art. It ishighly desirable in the whole food industry that raw materials havemeasurably homogeneous and consistent product properties. The maizeflour obtained by the present invention guarantees such a consistencyfor further processing such as the manufacture of tortilla. Inparticular, the viscosity, the elasticity and the color of a tortilladough could be significantly improved when it was produced from theflour according to the present invention.

Referring now to FIG. 1, a preferred embodiment of the invention isillustrated by a flow diagram. First, corn kernels are cleaned byconventional methods. Subsequently, the product undergoes a firstpreconditioning step, in which the product is moistened with water forabout 12 hours. Afterwards, the corn kernels are ground coarsely,preferably by a four-roller-mill. During coarse grinding, the particlesare ground to particle sizes in the range between 1000 and 6000 μm, morepreferably between 1500 μm and 5500 μm.

After coarse grinding, a fine fraction of the product may be removed byclassifying, in particular by air-classification or sieving, wherebyparticles below 1000 μm are removed, preferably below 1500 μm can beremoved.

During a subsequent second preconditioning step taking about 12 hours,the water content of the corn kernels is increased to 20-30 wt %. Thisfirst and second preconditioning may be performed in a DampenerTurbolizer MOZL or dampening screw NFAS obtainable from Bühler A G,Uzwil, Switzerland.

After said second preconditioning step, a lime solution is sprayed ontothe product. The lime solution comprises water and between 2 and 4% byweight of lime. The lime solution is added to the product in an amountof 2 to 6%, preferably 3 to 5% by weight of dry matter of maize. Thislime treatment may be performed by the POLYtherm™ BCTC preconditioner,obtainable from Bühler A G, Uzwil, Switzerland.

Afterwards, a steaming step is performed in a two-stage process. In thefirst steaming step, which may also be performed by the above-mentionedPOLYtherm™ BCTC, the product is heated to a temperature between 80 and105° C. The second, continuous steaming step may be performed by an MBDAsteamer, also obtainable from Bühler A G, Uzwil, Switzerland. In thesecond steaming step, the product is contacted directly with saturatedsteam at a temperature of 95-100° C. The ratio in the second steamingstep is 70 to 80% by weight of dry matter of the product to 20 to 30% byweight water. The water content of the product thereafter is 20 to 30%by weight.

The holding time after the two steaming steps takes most preferablyabout 90 minutes.

Next, a flaking step is performed by a flaking roller mill. This flakingstep may be performed by a POLYfloc™ BCFA Flaking Roller Mill, alsoobtainable from Bühler A G, Uzwil, Switzerland. Then, a first dryingstep is performed by hot air indirectly generated by an air-heater. Asecond drying step is conducted by a fluidized bed drier, preferably anOTW-Z obtainable from Bühler A G, Uzwil, Switzerland. After the dryingsteps, the product has preferably a water content of lower than 12 wt %.

Subsequently, cooling may be performed by cool-air drying of theproduct. A fine fraction can be removed in a classifying step.Preferably, a fraction comprising particles having sizes below 1000 μmcan be removed. A milling step guarantees a uniform productspecification at a certain degree of granulation. A hammer mill or aroller mill is suitable to perform this milling step in an accurate way.

The invention claimed is:
 1. Method for processing a maize corn productcomprising maize to produce a maize flour, said method comprising: atleast one preconditioning step, in which the maize corn product ismoistened to produce a preconditioned maize corn product; a subsequentat least one treatment step, in which an alkaline solution is sprayedonto the preconditioned maize corn product to produce a treated andpreconditioned maize corn product; a subsequent hydro-thermal treatmentstep, performed by steaming, in which the treated and preconditionedmaize corn product is contacted directly with steam at a temperature of80-105° C. to produce a steamed, treated and preconditioned maize cornproduct; a subsequent holding step, in which the steamed, treated andpreconditioned maize corn product is held for a holding time of at least10 minutes to produce a held, steamed, treated and preconditioned maizecorn product; and a subsequent milling step, in which the held, steamed,treated and preconditioned maize corn product is milled to produce themaize flour.
 2. Method according to claim 1, wherein the alkalinesolution is a lime solution.
 3. Method according to claim 2, wherein thelime solution comprises water and between 1 and 5% by weight of lime. 4.Method according to claim 3, wherein the lime solution is added to thepreconditioned maize corn product in an amount of 2 to 6% by weight ofdry matter of the maize.
 5. Method according to claim 4, wherein the atleast one preconditioning step takes between 2.5 and 12 hours.
 6. Methodaccording to claim 4, wherein the at least at least one preconditioningstep comprises a first preconditioning step, in which the maize cornproduct is moistened to produce a first preconditioned maize cornproduct; a subsequent coarse grinding step, in which thefirst-preconditioned maize corn product is ground coarsely to produce acoarsely ground first preconditioned maize corn product; and asubsequent second preconditioning step, in which the coarsely groundfirst-preconditioned maize corn product is moistened to produce thepreconditioned maize corn product.
 7. Method according to claim 6,wherein the coarse grinding step is performed by a roller mill. 8.Method according to claim 6, comprising a classifying step, whereinprior to the at least one treatment step, a fine fraction of either thecoarsely ground first-preconditioned maize corn product or thepreconditioned maize corn product is removed by classifying.
 9. Methodaccording to claim 1, wherein the hydro-thermal treatment step comprisesat least a first steaming step and a second steaming step.
 10. Methodaccording to claim 1, wherein at least a part of the steaming, at thehydro-thermal treatment step, is performed continuously.
 11. Methodaccording to claim 1, wherein during the hydro-thermal treatment step,the treated and preconditioned maize corn product is contacted directlywith saturated steam at a temperature of 95-100° C.
 12. Method accordingto claim 1, wherein during the hydro-thermal treatment step, the treatedand preconditioned maize corn product is contacted directly withsaturated steam for 30-90 minutes.
 13. Method according to claim 1,wherein the method comprises at least one flaking step in which theheld, steamed, treated and preconditioned maize corn product is flakedprior to the milling step.
 14. Method according to claim 1, wherein themethod comprises at least one drying step in which the held, steamed,treated and preconditioned maize corn product is dried prior to themilling step.
 15. Method according to claim 14, wherein the at least onedrying step is performed by hot-air drying.
 16. Method according toclaim 14, wherein the at least one drying step is performed in afluidized bed dryer or a roaster.
 17. Method according to claim 1,wherein the method comprises at least one cooling step prior to themilling step.
 18. Method according to claim 8, wherein, in theclassifying step, the removed fine fraction comprises particles havingsizes below 1000 μm.
 19. Method according to claim 1, wherein themilling step is performed in a hammer mill or a roller mill.
 20. Methodfor processing a maize corn product comprising maize to produce a maizeflour, said method comprising: at least one preconditioning step inwhich the maize corn product is moistened to produce a preconditionedmaize corn product; a subsequent at least one treatment step, in whichan alkaline solution is sprayed onto the preconditioned maize cornproduct to produce a treated and preconditioned maize corn product; asubsequent hydro-thermal treatment step, performed by steaming, in whichthe treated and preconditioned maize corn product is contacted directlywith steam at a temperature of 95-100° C. to produce a steamed, treatedand preconditioned maize corn product; and a subsequent holding step, inwhich the steamed, treated and preconditioned maize corn product is heldfor a holding time of at least 10 minutes to produce a held, steamed,treated and preconditioned maize corn product; and a subsequent millingstep, in which the held, steamed, treated and preconditioned maize cornproduct is milled to produce the maize flour.
 21. Method according toclaim 20, wherein the alkaline solution is a lime solution.
 22. Methodaccording to claim 21, wherein the lime solution comprises water andbetween 1 and 5% by weight of lime.
 23. Method according to claim 22,wherein the lime solution is added to the preconditioned maize cornproduct in an amount of 2 to 6% by weight of dry matter of the maize.24. Method according to claim 23, wherein the at least onepreconditioning step takes between 2.5 and 12 hours.
 25. Methodaccording to claim 23, wherein the at least one preconditioning stepcomprises a first preconditioning step, in which the maize corn productis moistened to produce a first preconditioned maize corn product; asubsequent coarse grinding step, in which the first-preconditioned maizecorn product is ground coarsely to produce a coarsely ground firstpreconditioned maize corn product; and a subsequent secondpreconditioning step, in which the coarsely ground first-preconditionedmaize corn product is moistened to produce the preconditioned maize cornproduct.
 26. Method according to claim 25, wherein the coarse grindingstep is performed by a roller mill.
 27. Method according to claim 25,comprising a classifying step, wherein prior to the at least onetreatment step, a fine fraction of either the coarsely groundfirst-preconditioned maize corn product or the preconditioned maize cornproduct is removed by classifying.
 28. Method according to claim 20,wherein the hydro-thermal treatment step comprises at least a firststeaming step and a second steaming step.
 29. Method according to claim20, wherein at least a part of the steaming, at the hydro-thermaltreatment step, is performed continuously.
 30. Method according to claim20, wherein during the hydro-thermal treatment step, the treated andpreconditioned maize corn product is contacted directly with saturatedsteam for 30-90 minutes.
 31. Method according to claim 20, wherein themethod comprises at least one flaking step in which the held, steamed,treated and preconditioned maize corn product is flaked prior to themilling step.
 32. Method according to claim 20, wherein the methodcomprises at least one drying step in which the held, steamed, treatedand preconditioned maize corn product is dried prior to the millingstep.
 33. Method according to claim 20, wherein the at least one dryingstep is performed by hot-air drying.
 34. Method according to claim 33,wherein the at least one drying step is performed in a fluidized beddryer or a roaster.
 35. Method according to claim 20, wherein the methodcomprises at least one cooling step prior to the milling step. 36.Method according to claim 27, wherein, in the classifying step, theremoved fine fraction comprises particles having sizes below 1000 um.37. Method according to claim 20, wherein the milling step is performedin a hammer mill or a roller mill.